1. Field of the Invention
The present invention relates to a method for reducing a poor pattern formation on a photoresist film by contacting the photoresist film with an alkaline solution prior to its exposure to light.
2. Description of the Background Art
In a conventional photoresist pattern formation process, a photoresist film is produced by depositing hexamethyldisilazane (HMDS) on a substrate to enhance the adhesiveness between the substrate and the photoresist composition. The photoresist film is then exposed to light and developed in tetramethylamoniumhydroxide (TMAH) solution to obtain a pattern.
In general, when there is a delay between exposure of the photoresist film to light and development of the exposed photoresist, acids that are generated on the exposed area are neutralized by amine compounds that may be present in the production atmosphere. Since the pattern formation depends on acids that are generated by the exposure, neutralization of acids by atmospheric amine compounds reduce, prevent or alter a pattern formation, e.g., a T-topping phenomenon may occur where the top portion of the pattern forms a T-shape. As a result, a post-exposure delay may result in a poor pattern formation and a gap formation in CD (Critical Dimension).
To reduce or prevent the above described problems, a top anti-reflective coating (hereinafter abbreviated as xe2x80x9cTop ARCxe2x80x9d) applied to the photoresist film has been used; however, in many cases the use of Top ARC results in a severe top loss in the upper portion of the photoresist film. In theory, an acidic Top ARC material will prevent a poor pattern formation by neutralizing the amine compounds, which may be present in the atmosphere, and thereby preventing the amine compounds from neutralizing the acids which are generated during the exposure. However, the use of an acidic Top ARC material results in even more severe top loss. Without being bound by any theory, it is believed that this is due to the fact that the acidic Top ARC materials contain carboxyl and hydroxyl groups which form hydrogen bonding with the acids that are generated during exposure. This hydrogen bonding effectively increases the concentration of the acid in the upper portions of the photoresist film. These acids then diffuse into the unexposed regions during post exposure bake (PEB) causing undesired top loss.
Therefore, there is a need for a method to reduce or prevent poor pattern formation and/or top loss of a photoresist film.
The present inventors have found that T-topping caused by post exposure delay and top loss caused by having Top ARC material coating on a photoresist film can be significantly reduced or eliminated by contacting the photoresist film with an alkaline solution prior to its exposure.